1. Field of the Invention
This invention relates to ignition systems for internal combustion engines and, in particular, to inductively coupled ignition systems for rotary combustion engines.
2. Description of the Prior Art
While rotary combustion engines offer some significant advantages over conventional reciprocating engines for automotive use, fuel economy and emission problems have delayed the widespread application of these power plants. The precise causes of poor fuel economy and emission difficulties are still being studied. It is clear, however, that the relatively large surface area to combustion volume ratios, shrouded ignition sources, and poor flame front propagation are primary causes of economy and emission problems in the Wankel engine, which is perhaps the most highly developed rotary to date.
Conventional rotary spark ignition engines such as the Wankel generally consist of a stationary outer housing and an internal rotating or oscillating member. As in conventional reciprocating engines, the spark duration is very short, for example, on the order of milliseconds, so that a plurality of plugs and plug holes are required for extended ignition periods. Spark ignition to such rotary engines is usually provided by one or more circumferentially located stationary spark plugs mounted in the outer housing assembly.
Recent engine designs included two spark plug ignition sources, a leading and trailing plug to assure adequate ignition of the mixture. Spark timing is a function of rotor speed and is controlled by two conventional distributors or by one "dual" distributor. The spark plugs communicate with the combustion chamber by means of touch holes in the trochoid housing. In practical engine designs, these holes are at a location and of a diameter which is at best a compromise of performance and efficiency. Ideally, the spark plug holes should be as large as possible so as not to shroud the plug yet not large enough to increase the unswept combustion volume or provide a leakage path past the apex seals.
In the Wankel engine, the spark plugs fire three times per rotor revolution and are never subjected to the cooling of the intake mixture. This continuous high temperature environment requires special premium plugs. Moreover, the shrouded plug tip is particularly susceptible to carbon fouling, since the electrodes are not located in the combustion volume per se and oil is added to the combustion mixture for seal lubrication.
Several attempts by various investigators have been made to remedy the difficulties encountered with peripheral plugs by locating the spark source on the rotor body. Means for high voltage transmission to the rotor assembly have been incorporated on the rotor shaft. Separate high voltage slip rings and sliding contacts must be provided for each spark plug to prevent the spark plugs from firing simultaneously. In this case, spark timing still required an external distributor or a mechanical spark advance mechanism on a high voltage commutator while insurmountable difficulties in high voltage insulation and distribution precluded the effective transmission of spark voltages to the rotor. As a result, no successful application of rotor mounted spark plugs has been made to date.
The invention described herein makes possible the use of rotor mounted spark plugs with none of the attendant difficulties in handling the high voltages. In addition, the invention eliminates the use of distributors or mechanical spark timing apparatus, while permitting spark durations of up to 90.degree. of crank rotation.